1. Field of the Invention
This invention relates to a thermosetting enamel coating composition wherein low molecular weight polyester and addition polymers that have controlled hydroxyl-functionality are crosslinked at cure with aminoplast resins.
2. Description of the Prior Art
Conventional enamel coating compositions have been produced using hydroxyl-functional acrylic and polyester components that are thermoset by crosslinking with aminoplast resins. Such coatings have highly desirable properties in most instances and are therefore quite useful for specific applications. For example, U.S. Pat. No. 4,076,766, issued Feb. 28, 1978 to Simms discloses such a coating composition useful for coating flexible materials.
In past attempts to use thermosetting acrylic-polyester coating compositions as automotive finishes, the problem of having to sacrifice one desirable quality to enhance another has often been encountered. For example, compositions that are high in acrylic content normally have high gloss but may be susceptible to low-temperature cracking. Those high in polyester content may not suffer this problem, but may exhibit a loss of gloss upon sanding. Further complications arise from the current emphasis on reduction of solvent emissions, which often requires high solids levels in the coating compositions. High solids thermosetting coating compositions have in the past often lacked the flexibility and aesthetic qualities necessary for use as automotive finishes.
Therefore, there remains a need for a thermosetting enamel coating composition that can be applied at high solids levels and that also retains the other qualities necessary in an automotive finish.